Pasivirus

VIRION

Non-enveloped, spherical, about 30 nm in diameter, T=pseudo3 icosahedral capsid surrounding the naked RNA genome. The capsid consists of a densely-packed icosahedral arrangement of 60 protomers, each consisting of 3 polypeptides, VP0, VP1 and VP3. There is no internal capsid protein.

GENOME

Monopartite, linear, ssRNA(+) genome of 7.3 kb, polyadenylated, composed of a single ORF encoding a polyprotein. Viral genomic RNA has a viral protein (VPg) at its 5' end instead of a methylated nucleotide cap structure. The long UTR at the 5' end contains an internal ribosome entry site (IRES). The P1 region encodes the structural polypeptides. The P2 and P3 regions encode the nonstructural proteins associated with replication. Encodes a unique protease 3C (2A2 lacks proteolytic activity). The shorter 3' UTR is important in (-)strand synthesis.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. The IRES allows direct translation of the polyprotein. The polyprotein is initially processed by the viral protease into various precursor and mature proteins to yield the structural proteins, replicase, VPg, and a number of proteins that modify the host cell, ultimately leading to cell lysis. Ribosomal skipping is probably used at the junction of the 2A and downstream sequence.